1. Field of the Invention
The present invention relates in general to electric valve timing control devices of an internal combustion engine, and more particularly to the electric valve timing control devices of a type that continuously varies open/close timing of engine valves (viz., intake valves and/or exhaust valves) with the aid of a phase varying mechanism powered by an electric motor.
2. Description of the Related Art
Hitherto, various timing control devices of an internal combustion engine have been proposed and put into practical use in the field of wheeled motor vehicles powered by the internal combustion engine. Some of them are of an electric type that exhibits a satisfied control response and controllability with the aid of a phase varying mechanism powered by an electric motor.
In some of the electric valve timing control devices of such type, the electric motor is constantly energized for rotation while a sprocket driven by a crankshaft of the engine rotates. This means that under operation of the engine, the electric motor is kept energized, which however brings about a marked energy loss of the engine.
Japanese Laid-open Patent Application (Tokkaihei) 11-107718 shows an electric valve timing control device that is constructed to eliminate or at least minimize the above-mentioned energy loss of the engine. In the control device of the publication, slip rings and brushes are employed for feeding the electric motor with an electric current and only when changing of the valve timing is needed, the electric motor is energized for rotation.